首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3065篇
  免费   151篇
  国内免费   18篇
耳鼻咽喉   35篇
儿科学   57篇
妇产科学   10篇
基础医学   591篇
口腔科学   30篇
临床医学   190篇
内科学   747篇
皮肤病学   27篇
神经病学   327篇
特种医学   71篇
外科学   435篇
综合类   9篇
预防医学   62篇
眼科学   48篇
药学   282篇
中国医学   5篇
肿瘤学   308篇
  2023年   21篇
  2022年   39篇
  2021年   64篇
  2020年   25篇
  2019年   44篇
  2018年   65篇
  2017年   33篇
  2016年   57篇
  2015年   46篇
  2014年   80篇
  2013年   96篇
  2012年   170篇
  2011年   218篇
  2010年   92篇
  2009年   102篇
  2008年   169篇
  2007年   167篇
  2006年   203篇
  2005年   174篇
  2004年   189篇
  2003年   195篇
  2002年   161篇
  2001年   64篇
  2000年   59篇
  1999年   62篇
  1998年   66篇
  1997年   38篇
  1996年   41篇
  1995年   31篇
  1994年   36篇
  1993年   35篇
  1992年   63篇
  1991年   43篇
  1990年   38篇
  1989年   34篇
  1988年   30篇
  1987年   25篇
  1986年   19篇
  1985年   21篇
  1984年   16篇
  1983年   10篇
  1982年   7篇
  1981年   11篇
  1980年   8篇
  1979年   11篇
  1978年   12篇
  1977年   7篇
  1976年   9篇
  1973年   5篇
  1970年   5篇
排序方式: 共有3234条查询结果,搜索用时 15 毫秒
1.
A Bochdalek hernia (BH) is a congenital abnormality with incomplete closure of the diaphragm. It is usually manifested in infants but rarely in adults. Here, we report an adult patient with gastric volvulus and giant BH that were safely repaired by endoscopic reduction and elective laparoscopic surgery, respectively. A 79-year-old woman presented with left upper abdominal pain but no history of trauma. CT revealed a giant BH with gastric volvulus. After emergency endoscopic reduction of the volvulus, elective laparoscopic repair of the BH was performed. The 8 × 8-cm defect was repaired with interrupted nonabsorbable sutures and a mesh. The patient's postoperative course was uneventful, and no complications or recurrence were observed in the 6 months that followed.  相似文献   
2.
A 1:1 adduct of methyl sorbate (MS) and 1,3‐di‐tert‐butylimidazol‐2‐ylidene (NHCtBu) initiates anionic polymerization of a nonconjugated polar alkene, allyl methacrylate (AMA) in toluene at ?20 °C. After the monomer is consumed quantitatively using a bulky aluminum Lewis acid, methylaluminum bis(2,6‐di‐tert‐butyl‐4‐methylphenoxide) (MAD), as an additive, successive ring‐closure occurs without highly dilute conditions to give a cyclic poly(AMA) containing α‐terminal MS unit, and an Mn of 8.8 × 103?58.5 × 103 with a narrow molecular dispersity index (Mw/Mn = 1.14–1.37). The lack of a need for dilution is due to the fact that an α‐terminal NHCtBu group is acting as the counter cation for the propagating center in the polymerization. From 1H NMR and matrix assisted laser desorption/ionization (MALDI‐TOF) mass spectra, combined with transmittance electron microscope (TEM) observation of a synthesized poly(AMA) with longer alkyl side chains prepared via a thiol‐ene click reaction, it is concluded that once the monomer is consumed, nucleophilic attack at the neighboring methine of the α‐terminal NHCtBu residue by the propagating anionic center causes ring‐closing to cyclic poly(AMA).  相似文献   
3.
OBJECTIVE: The Karolinska sleepiness scale (KSS) is frequently used for evaluating subjective sleepiness. The main aim of the present study was to investigate the validity and reliability of the KSS with electroencephalographic, behavioral and other subjective indicators of sleepiness. METHODS: Participants were 16 healthy females aged 33-43 (38.1+/-2.68) years. The experiment involved 8 measurement sessions per day for 3 consecutive days. Each session contained the psychomotor vigilance task (PVT), the Karolinska drowsiness test (KDT-EEG alpha & theta power), the alpha attenuation test (AAT-alpha power ratio open/closed eyes) and the KSS. RESULTS: Median reaction time, number of lapses, alpha and theta power density and the alpha attenuation coefficients (AAC) showed highly significant increase with increasing KSS. The same variables were also significantly correlated with KSS, with a mean value for lapses (r=0.56). CONCLUSIONS: The KSS was closely related to EEG and behavioral variables, indicating a high validity in measuring sleepiness. SIGNIFICANCE: KSS ratings may be a useful proxy for EEG or behavioral indicators of sleepiness.  相似文献   
4.
To elucidate the growth of the tarsal bones in congenital clubfoot, relative to the growth of these bones in the unaffected feet and compared to growth in the feet of normal volunteers, we used a computed tomography (CT) scanner to measure the volume of all tarsal bones. The subjects of the study were 10 adults (7 men and 3 women) with unilateral congenital clubfoot (average age 20 years and 1 month). As controls, we examined 11 healthy volunteers. We calculated the ratio of the volume of each tarsal bone to the total bone volume and the ratio of the volume of each tarsal bone in clubfoot to the corresponding bone in the unaffected foot. The volume ratio of each tarsal bone was compared between clubfeet and unaffected feet because the differences of each tarsal bone ratio between the normal foot group and unaffected foot group were not significant. In the clubfeet (n=10), the talus and the medial cuneiform bones were smaller than those in the unaffected feet (n=10) but the cuboid bone was larger. The growth of the navicular did not differ from as that in unaffected feet. Our results suggested hypoplasia on the medial side of the foot in adult patients with congenital clubfoot. The 3 patients who had undergone medial release showed particularly marked hypoplasia of the medial side. In congenital clubfoot cases with severe deformities who had undergone wide soft-tissue release operations, there were clear growth suppressions in the talus and the medial cuneiform. We could not determine whether the cause of the growth suppression was the hypoplastic nature of tarsal bones themselves or the surgical obstacles to tarsal bone growth.  相似文献   
5.
The effects of KB-2796, 1-[bis(4-fluorophenyl)methyl]-4-(2,3,4-trimethoxybenzyl)piperazine-2HCl, on the low- and high-voltage activated Ca2+ currents (LVA and HVA ICa, respectively) and on oxidative metabolism were studied in neurons freshly dissociated from rat brain. KB-2796 reduced the peak amplitude of LVA ICa in a concentration-dependent manner with a threshold concentration of 10−7 M when the LVA ICa was elicited every 30 s in the external solution with 10 mM Ca2+. The concentration for half-maximum inhibition (IC50) was 1.9 × 10−6M. At 10−5 M or more of KB-2796, a complete suppression of the LVA ICa was observed in the majority of neurons tested. There was no apparent effect on the current-voltage (I-V) relationship and the current kinetics. KB-2796 delayed the reactivation and enhanced the inactivation of the Ca2+ channel for LVA ICa voltage- and time-dependently, suggesting that KB-2796 preferentially binds to the inactivated Ca2+ channel. KB-2796 at a concentration of3.0 × 10−6M also decreased the peak amplitude of the HVA ICa without shifting the I-V relationship. In addition, KB-2796 reduced the oxidative metabolism (the formation of reactive oxygen species) of the neuron in a concentration-dependent manner with a threshold concentration of3 × 10−6M. It is suggested that the inhibitory action of KB-2796 on the neuronal Ca2+ influx and the oxidative metabolism, in combination with a cerebral vasodilatory action, may reduce ischemic brain damage.  相似文献   
6.
The matrix metalloproteinase matrilysin (MMP-7) is a member of the matrix metallo-proteinase gene family, which is believed to play an important role in tumor invasion and metastasis. We have previously found that matrilysin mRNA is specifically expressed in colorectal cancers and adenomas and that its message is localized in the tumor cells themselves. We examined the effects of activated Ki-ras oncogene on the expression of matrilysin in colon cancer cells. We showed that both mRNA and the enzymatic activity of matrilysin were induced by the introduction of activated Ki-ras into SW1417 colon cancer cells. To understand the mechanisms regulating this induction, we analyzed alterations of AP-1 activity induced by activated Ki-ras, using the chloramphenicol acetyltransferase assay. AP-1 activity in SW1417 cells expressing activated Ki-ras was higher than that in control cells. The gel-shift assay also showed higher levels of AP-1 binding protein in SW1417 cells expressing activated Ki-ras than those in control cells. Our results suggest that activated Ki-ras may play a role in inducing expression of matrilysin through an AP-1-dependent pathway in colon cancer cells.  相似文献   
7.
Electroencephalographic (EEG) studies were performed to examine the effects of SM-3997 on the spontaneous EEG, EEG arousal responses, recruiting responses and hippocampal afterdischarges in rabbits and the spontaneous EEG in chronically electrode-implanted rats. In acute experiments using rabbits, SM-3997 at doses of 1-3 mg/kg, i.v., produced low-voltage fast waves in cortical EEG and slow waves with reduction of the amplitude in hippocampal EEG. The drug at doses of 1-3 mg/kg, i.v., dose-dependently inhibited the threshold stimulus voltages in EEG arousal responses induced by stimulation of the midbrain reticular formation and slightly inhibited the threshold in recruiting responses by stimulation of the centromedian nucleus of the thalamus. However, the cortical and hippocampal afterdischarges induced by hippocampal stimulation remained unaffected by SM-3997 at doses up to 3 mg/kg, i.v., while they were inhibited by diazepam of 1 mg/kg, i.v. In the study using rats in which electrodes were chronically implanted, SM-3997 at doses of 10-30 mg/kg, i.p., also produced low voltage fast waves in cortical EEG and slow waves of reduced amplitude in hippocampal EEG; and it simultaneously caused flat body posture. These results suggest that SM-3997 acts on both the cerebral cortex and hippocampus, inducing much more pronounced inhibition on the midbrain reticular formation-hippocampal system  相似文献   
8.
9.
A patient with a recurrent tumor in the trachea adjacent to the right main bronchus was treated by surgical resection 19 months after undergoing surgery for the primary cancer. The patient had previously undergone right upper lobectomy for T1N0M0 stage I squamous cell carcinoma. A carinal resection was performed which included 4 rings of the trachea, 2 rings of the righ main bronchus, and 1 ring of the left main bronchus. Reconstruction consisted of an end-to-end anastomosis of the trachea and left main bronchus, and an end-to-side anastomosis of the right and left main bronchi. The postoperative course was uneventful, and at present the patient is healthy 12 months following reoperation.  相似文献   
10.
The characteristics of neuronal and paraneuronal muscarinic inhibition and excitation were analyzed using rat caudate nucleus (CN) slices and isolated chromaffin cells obtained from the rat adrenal medulla. In CN neurons, either acetylcholine (ACh), carbachol, or muscarine inhibited orthodromically activated firing, while nicotine had no effect on neuronal activity. Muscarine decreased the amplitude of EPSPs without altering the resting membrane potential (RMP), input impedance and EPSP time courses. These results indicate that muscarinic receptors produce the presynaptic inhibition of synaptic transmission in the CN. In adrenal chromaffin cells, it was found that ACh, muscarine, and nicotine all increased extracellularly recorded firing. During voltage clamp recording at the RMP, ACh induced a transient inward current (fast response) followed by a long-lasting current (slow response). Muscarine induced the slow response, whereas nicotine induced the fast response. Muscarine reduced the inward K+ current produced by the application of a high K+ medium to cells. During patch clamp recording, muscarine decreased the opening rate of the single K+ channels. These results indicate that the muscarinic excitation of adrenal chromaffin cells was triggered by a reduction in the number of active K+ channels at the RMP.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号